Process of extruding steel



United States Patent PROCESS OF EXTRUDING STEEL Elliot S. Naclltman, Park Forest, and Eldon B. Moore, Calumet City, 111., assignors to La Salle Steel Company, Hammond, Ind., a corporation of Delaware N0 Drawing. Application June 27, 1955, Serial No. 518,413

13 Claims. (Cl. 207-) This application is a continuation-in-part of our copending applications Ser. No. 293,431, filed June 13, 1952, and entitled Metallurgical Process and Steel Products Produced Therefrorn, and Ser. No. 293,432, filed June 13, 1952, and entitled Metallurgical Process and Steel Products Produced Therefrom, both now abandoned.

It is an object of this invention to produce and to provide a new and improved metallurgical process for producing steels of the type described, especially steels of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, characterized by improved machinabil-ity.

Another object is to provide a new and improved process for introducing improved physical properties in steel while concurrently incorporating improved mechanical properties such as are incapable of being produced by processes h-ereinto-fore employed, particularly with respect to such properties as tensile strength, proportional limits, and hardness with and without noticeable effect on the ductility of the steel, thereby to achieve the production of a new and improved steel of the type described.

A further object is to provide a metallurgical process for producing steels embodying characteristics of the type described by the simple medium of working the steel as by drawing or extrusion without noticeable increase in warping value and more particularly with reduced residual stresses and stress control without the necessity for additional steps heretofore employed for stress relieving drawn steel.

As used herein, the term machinability is intended to define the ability of the metal to be cut, ground or processed by machine tools normally used in the fabrication of steel products. Machinability characteristics, as defined herein, are evaluated by comparison of the steel as against a standard specimen mounted on a lathe and cut with a non-driven tool. Constant pressure is asserted on the lathe tool as it cuts. This constant pressure of the cutting tool causes widely varying feeds depending upon the m-achinability of the metal being tested and, when everything else is held constant, the feed rate may be taken as a measurement of the machinability of the steel.

The physical property of surface roughness constitutes a measurement taken by means of a profilometer, which measures the surf-ace of the roughness in terms of microinches.

As used herein, the term mechanical properties is intended to include such properties as tensile strength, yield strength, proportional limit, impact strength, and hardness.

The term proportional limit corresponds to the point in the stress-strain curve where the greatest stress that the material is capable of sustaining without deviation 2,767,836 Patented Oct. 23, 1956 from the law of proportionality of stress to strain occurs. (Hookes Law.) This point is of particular importance in steel and, in particularly every instance, is measurably increased to heretofore unobtainable high values when the steels of the non-austenitic type are produced, as by drawing or extrusion, at elevated temperatures within the range defined in the aforementioned copending applications.

In said copending applications, description is made of a new and improved metallurgical process wherein properties heretofore secured only by taking abnormally heavy drafts and stress relieving, such as described in the Landis Patent No. 2,320,040, wherein description is made of a process for cold finishing of steel as by drawing toproduce a smooth and satisfactory surface finish, are capable of being equalled and, in most instances, surpassed by a more simplified and more economical process embodying the features of this invention wherein the steel is heated for drawing to a temperature above 450 lower critical temperature for the particular steel composition, such as at a temperature below 1100-1200 F. For the particular properties which it is desired to develop in the steel in accordance with the practice of this invention, it is preferred to work the steel as by drawing within the temperature range of 600850 F. It has been found that by reason of the temperature and the pressures asserted by the drawing die, such reactions take place in the steel as to embody stress relieving concurrently and in combination with the development of the described improvements in physical and mechanical properties and in the machinability of the steel.

As to the mechanical properties, it has been found that by drawing at elevated temperatures within the range defined,

strength properties, proportional limits and hardness comparable nonaustenitic steels for the more expensive heat treated steels or for the more costly and less available alloy steels.

One of the principal improvements herein resides in the discovery that there is a relationship between the temperature of the steel drawn, the amount of draft and the chemistry of the steel for the development of optimum values in particular mechanical properties. For example, it has been found that where a non-austenitic type steel, heated to within a temperature range of 450-850 F., is drawn with abnormally heavy drafts, extremely high tensile strengths and hardness values can be obtained where appropriate temperature is employed for the steel.

In contrast to the multiple steps heretofore employed in prior art processes, mechanical properties far superior to those secured by such multiple operations can be secured, in accordance with the practice of this invention, in a single operational step simply by drawing the steel under controlled temperature conditions whereby, in addition to the improvement of mechanical properties, the drawn steel products are characterized by less Warpage when drawn at the appropriate temperatures.

It has also been found that by proper control of temperature and draft, new and unexpected proportional limits and yield strengths are capable of being developed in steels of the non-austenitic type having a pearlitic structure in a matrix of free ferrite. As would be expected, proportional limits and yield strengths parallel each other in many respects. It has been found that by heating the F. but below the r it is possible by taking normal drafts to achieve steel to a temperature within the range of 450850 F., and preferably to a temperature within the range of 600-850 F., superior results are secured both in proportional limits and yield strengths and heating the steels to temperatures above or below the defined range for drawing causes yield strengths to be reduced although the ductility may be. further increased. The development in such unexpected properties and yield strengths and proportional limits is dependent somewhat on the amount of draft, the temperature at which the optimum properties are secured and the chemistry of the steel.

The process to improve the physical and mechanical properties of steels of the type described, such as are secured by working as by drawing or extrusion of the steels at elevated temperatures within the range described, can advantageously be further divided depending upon the elastic properties desired in the end product. It has bee found further that it is possible to control precipitation hardening to any desired extent where one has available the desirable amount of work hardening and precipitation hardening. When the steel is worked, as by drawing or extrusion, to effect reduction in crosssectional area while the steel is at a temperature of 600 F. or above, the elastic properties of the steel produced is improved. Processing of the steel at a temperature below 600 F. results in decreasing the elastic properties of the steel. In other words, ductility of the steel produced or its measurable elastic properties are maximized while still achieving the other desired improvements in machinability and mechanical and physical properties when the steel is drawn at a temperature above 600 F. and preferably below 850 F.

This may be illustrated by the data which will hereinafter be set forth. The property of elongation, which will be referred to in the data, illustrates the improvements obtained in ductility or in the steel. Thus for steels having improved ductility coupled with other improvements in mechanical and physical properties, it is desirable, in accordance with the practice of this invention, to work the steel, as by drawing, at a temperature within the range of 600-850 F. When it is desirable to produce steels for certain uses having strength properties with lesser ductility, it is preferred to process the steel, as by drawing or extrusion to effect reduction in cross-sectional area, while at a temperature below 600 F. but preferably above 450 F., as described and claimed in our copending application filed concurrently herewith.

As previously pointed out, machinability of the steels may also be improved by processing the steels in the manner described for improvement of the mechanical and physical properties. Some of the non-austenitic steels appear to be substantially insensitive to the temperature of drawing as regards their machinability characteristics but important improvements in machinability may be caused to result in steels of other chemistries when drawing is effected within .a well defined temperature range thereby further to improve the metallurgical treatment of steels to make them more readily adaptable for subsequent use.

From the practical standpoint, it is known that for some grades of non-austenitic steel having more than 0.10 percent carbon but less than 0.65 percent and preferably less than 0.5 percent carbon, the machinability of the steel is increased by drawing at a temperature within the range of over 450 F. to about 850 F. Within this range, very important and marked improvements in machinability result in non-resulphurized low sulphur steels having a carbon content between 0.10 and 0.35 percent by weight.

Typical of the steels in which the improvements in physical and mechanical properties are capable of being developed in the manner herein described are steels which can be strain hardened and which harden by some mode of precipitation at temperatures below the lower critical the elastic properties of temperature. If the steel shows hardening because of precipitation or other re-arrangement, then it becomes possible to improve the strength properties and the physical properties of the steel by the practice of this invention wherein the steel is drawn at elevated temperatures to effect reduction in cross-sectional area.

From actual experimentation, it is also known that with non-austenitic steels containing freeferrite capable of hardening by strain and age hardening,.unexpected improvements in physical properties are secured by working at temperatures capable of hardening the free ferrite. In steels having little or no free ferrite in their structures, machinability appears to be substantially unaffected by temperature of drawing. On the other hand, nonaustenitic steels containing substantial amounts of free ferrite hardened during the drawing operation exhibit marked improvements in machinability by proper control of, the temperature of drawing to above 450 F. but below 850 F., particularly in non-austenitic steels having a carbon content between 0.10 and 0.35 percent.

Whilethe improvements in machinability depend somewhat upon the chemistry of the steel, the amount of draft and the temperature conditions existing during the drawing operation, surface roughness appears not to be so dependent, although surface roughness is vastly improved by working the steel at elevated temperatures.

The following examples will illustrate the concepts of this inventionas related to the property of machinability of steels in which the major ingredients other than iron are set forth.

EXAMPLE 1 In one series of tests, hot rolled Bessemer screw stock steel, 21 free machining grade of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, was drawn at various temperatures to achieve a 19 percent reduction from inch rounds. The composition of the steel is as follows:

008 percent carbon 0.75 percent manganese 0.12 percent phosphorus 0.27 percent sulphur 0.01 percent silicon 0.015 percent nitrogen EXAMPLE 2 0.48 percent carbon 1.50 percent manganese 0.03 percent phosphorus 0.27 percent sulphur 0.30 percent silicon 0.005 percent nitrogen EXAMPLE 3 In a third series of tests, hot rolled open hearth low sulphur steel of relatively poor machinability of the nonaustenitic type was drawn under the conditions of Examples 1 and 2 to achieve a similar reduction from inch rounds. The composition of this steel is as follows:

0.17 percent carbon 0.75 percent manganese 0.03 percent phosphorus 0.04 percent sulphur 0.08 percent silicon 0.005 percent nitrogen the compositions above Other bars of each composition" were heated to various temperature levels and then passed through the same Table I.Comparisn of machinability with various steels drawn at various temperatures Machinability rating in percent based on B1112 as 100 percent Temp. of Steel drawn F.)

Steel of Steel of Steel of Example 1 Example 2 Example 3 It Wlll be apparent from the results that the Bessemer steel composition of Example 1, characterized by a carbon content of less than 0.10 percent and a relatively high phosphorus and sulphur content, enjoys high machinability which is not profoundly influenced by this process. On the other hand, the composition of the open hearth low phosphorus and low sulphur steel of Example 3, having a carbon content of 0.17 percent, depends upon a predetermined balance of temperature, draft and chemistry to secure marked improvements in machinabili-ty. When drawing steel of the type of composition 3 at a temperature between 75-450 F., machinability ratings of only 3 are obtained. However, in'accordance with the practice of this invention, when the same steel is drawn at temperatures within the range defined herein, the machinability rating of the drawn steel is increased markedly to a value of about 62. Such improvement in machinability at temperatures within the range of 450- 850 F. constitutes a very important factor with respect to the wider application of such steel and the ability to machine the new high strength steel. It also is reflected in marked savings in scrap or loss of parts due to breakage, cracking or failure. The chemistry of the steel of Example 2, which is a medium carbon high sulphur steel, is such as to provide for some improvement in machinability at temperatures within the range of 450-850 F. When the steels of Examples 2 and 3 are heated totemperatures in excess of 840 F. for drawing, the machinability drops significantly and renders metallurgical treatment of such temperature ranges impractical where machinability might be of importance.

The following examples will illustrate the improvements which are secured in the hardness and in the proportional limits of steels embodying the features of this invention:

EXAMPLE 4 Steel Composition:

0.08 percent carbon 0.75 percent manganese 0.12 percent phosphorus 0.27 percent sulphur 0.01 percent silicon 0.015 percent nitrogen EXAMPLE 5 Steel Composition:

0.17 percent carbon 0.75 percent manganese 0.03 percent phosphorus 0.04 percent sulphur 0.08 percent silicon 0.005 percent nitrogen 'EXAMPLEG? Steel Composition:

0.48 percent carbon 1.50 percent manganese 0.03 percent phosphorus 0.27 percent sulphur 0.30 percent silicon 0.005 percent nitrogen Procedure.-Steel bars of the above compositions produced by conventional hot rolling practice so that they have a normal pearlitic and ferritic structure were advanced through a drawing die to achieve a 19 percent reduction in cross-sectional area from bars of inch round. One set of bars were drawn with lubricant on the surface but, without any previous heating to elevated temperature. Other bars were drawn through the same die with the same lubricant but heated for drawing to various elevated temperatures ranging up to about 1050 F. Hardness and proportional limits were determined for each and the values are listed in the following table for purposes of illustrating the effect of temperature control and chemistry on the development of such physical properties in steels of the types described.

Table II Brinell Hardness Proportional limits Surface Roughness (1,000 p. s. 1.) Temp. of steel drawn (F.) Steel Steel Steel Steel Steel Steel Steel Steel Steel of of of of of, of of of Ex.4 Ex.5 Ex.6 Ex.4 Ex.5 Ex.6 Ex.4 Ex.5 Ex.6

It will be observed from the above that with bars drawn to a 19 percent reduction in cross-sectional area within the temperature range of 450750 F., the hardness and proportional limits are at considerably higher values than those which are secured at temperatures below and above the described range.

The improvements in the mechanical and physical properties and the improvement in ductility of the steel when drawn at a temperature above 600 F. concurrently with the improvements in mechanical and physical properties can be illustrated by the following tables with non-austenitic steels of the type described including low alloy steels.

EXAMPLE 7 Steel composition:

0.16 percent carbon 0.71 percent manganese 0.01 percent phosphorus 0.03 percent sulphur 0.25 percent silicon 0.005 percent nitrogen Procedure.Bars of the above steel composition were given a 5 percent reduction by drawing 78 inch bars to approximately inch or about a inch draft at various temperatures ranging from room temperature up to about 900 F. Another set of bars /2 inch in diameter were given a 30 percent reduction by drawing to about inch or nearly a inch draft at the various temperatures. Drawing was effected at a speed of about 10 feet per minute using a lubricant such as Sinclair Oil Company No. L571. 7

Table lIl.-5 percent reduction Tabl-Vll-5 percent reduction Tensile Yield: Elong, Tensile Yield Elong. strength, strength; 1 Warpage strength, strength, 1%", Warpmze p. s. 1. 13.5. 1. percent Factor 5 p. s. 1. p. s. 1. percent Factor Hot Rolled Material..." 60,000 50,000 30 +.056 Hot Rolled Material..... 146,250 102,000 17, 5 +010 Temp. 01 Draw, F.: Temp. Draw, F.:

Table VIII .-30 ercent reduction Table I V .-30 percent reductmn 15 p Tensile Yield Elollg. Tensile Yield Elong. strength, strength, 1%", Warpage strength. strength, 1 Warpage p. s. i. p. s. 1. percent Factor p. s. l. p; s. 1. percent Factor 0 Hot Rolled Material..." 140,250 102,000 17. 5 010 Hot Rolled Material"... 60, 000 50,000 36 056 Temp. of Draw,'F.: Temp. 01' Draw, F.: 179, 500 131, 250 8 +459 200 95, 250 04, 750 14 218 197, 750 147, 250 0 302 109, 000 106, 500 11.5 172 198,250 180, 000 7 330 111,250 100,750 12. 5 190 169, 500 147, 250 12. 5 374 112,250 110,000 11.5 210 168, 000 142,250 13 377 103,750 101,250 13 201 151,250 134, 000 10. 5 210 96, 250 01, 000 17.5 +.1s7 150,500 130, 500 17.5 +111 03, 500 88, 000 10 14s 33, 750 84, 000 20 000 EXAMPLE 10 EXAMPLE 8 Steel composition: Steel composition: .63 percent carbon 0.44 percent carbon .92 perccnt'mangancsc 1.52 percent manganese .021 percent phosphorus 0.18 percent phosphorus .025 percent sulphur 0.31 percent sulphur .29 percent silicon 0.25 percent silicon .83 percent chromium 0 c 0 0 5 pm: at nitrogen Procedure.-Thc same procedure was followed for Same Procedum was followed for testing as in Example 7 except that the amounts of retastmg as Example ductions were 6.7 percent and 25 percent.

Table V.5 ercent reduction p Table IX .-6.7 percent reduction Tensile Yield Elong. strength, strength, 1% Wflrlmge Tensile Yield Elong.

D L D- S- Percent Factor strength, strength, 2, Walrpage p. s. i. p. s. 1. percent Factor got Rollfetlghiate ripln... 113,500 70,250 23 032 0 m 0 Mr Hot rolled material 14 ,7'0 80, 00 13 .(28

222s 12 551,45 Temp-0mm. 1 Y 12 163,750 140, 000 8 .4-4 138, 250 133, 250 10 617 1 2 0 15 00 3 34 132, 000 121, 250 13 579 1 5 0 55 000 c 5 126. 750 111, 250 15 427 7 500 1G3 900 6 8 120,000 10?,250 16 170, 250 102,000 7 5 +370 000 0 19 152 150, 250 100, 000 s 414 107, 500 152,500 8 +.412

Table VI.-30 percent reduction Tabl X .'--25 percent reduction Tensile Yield Elong. strength, strength, 1%, Warpage p. s. i. p. s. 1. percent Factor Tensllc Yield Elong.

strength strength 2", Warpn :0

p. s. i. p. s. 1. percent Factor Hot Rolled Materinl..... 113, 500 76,250 23 032 Temp. 01 Draw F.:

210... 141, 750 108,750 10 310 Hot rolled material 146, 750 80,500 13 023 400.. 157,000 133, 500 s 242 Temp. 01 Draw, "F 570.. 161,000 141, 250 5 256 40 179,250 156,000 7 232 620.. 105, 500 142, 500 8 +.143 178, 000 172,500 0 254 700.. 154, 500 137, 750 10 200 187, 500 180,000 5 243 780.. 145,500 129, 000 13 156 178, 500 160, 000 0 +136 920 120,000 107,500 19 030 174,250 156,000 10 +143 EXAMPLE 9 EXAMPLE 11 Steel composition: Steel composition:

.42 percent carbon .39 percent carbon .87 percent manganese .92 percent mangancsc .016 percent phosphorus .014 percent phosphorus .026 percent sulphur 7o .044 percent sulphur .29 percent silicon 1 .22 percent silicon .87 percent chromium .45 percent nickel .20pcrcent molybdenum .45 percent chromium Pf0Cdllf.-ThBl.1OW alloy 'steelof the above compopercent molybdenum sition was processed for testing as dcscribediu Examplcel. Procedure.-Thc same procedural was: followed; for

Table XI.-10 percent reduction Tensile Yield Elong. strength, strength, 2", Warpage p. s. i. p. s. i. percent Factor Hot rolled material 124, 330 110, 800 16 004 Temp. of Draw, F.:

Table XII.35 percent reduction Tensile Yield Elong. strength, strength, 1%, Warpage p. s. i. p. s. it percent Factor Hot rolled material 124, 330 110, 800 20 004 Temp. of Draw, F-1

EXAMPLE 12 Procedure.-The same procedure was followed for testing as in Example 7 except that reductions of 6.7 and 25 percent were taken.

Table XIII.6.7 percent reduction Tensile Yield Elong. Warpage strength, strength, 2", Factor p. s. i. p. s. i. Percent Hot Rolled Material- 125, 500 82, 500 20 048 Temp. of Draw, F.:

Table XIV.25 percent reduction Tensile Yield Elong. Warpage strength, strength, 2", Factor p. s. l. p. s. i. Percent Hot Rolled Material. 125, 500 82, 500 20 048 Temp. of Draw, F.:

It will be observed from the foregoing tables that the tensile strengths and yield strengths are markedly increased by drawing steels of the type described to eifect reduction in cross-sectional area While the steels are heated to a temperature within the range of 450 F. to

10 about 850 F. It will be observed also that at tempera' tures below 600 F. the percent elongation of the steels decreases, indicating a decrease in the elastic properties whereas the percent elongation begins to increase materially when the steel is drawn above 600 F. Thus steels are produced having improved physical properties and mechanical properties concurrently with maximized elasticity and steels may be produced for other purposes having similarly improved physical and mechanical properties concurrently with reduced elasticity merely by the proper selection of the temperature for drawing the steel.

The method of heating the steel to the desired temperature of drawing is unimportant. Heating may be achieved by any number of ways well known in the art, such as by an electric furnace, resistance heating or the like. For example, the steel may be heated by means of a salt bath which may advantageously be used also to coat the metal with a lubricant and otherwise condition the surface of the steel for drawing, as described in the copending application of Nachtman, Ser. No. 286,039, filed May 3, 1952, wherein description is made that, in the past, the metal has been prepared for deformation to produce a better finish in a cold finishing operation by treating the surface of the metal first with an acid to remove scale, followed by a rinse to remove acid, followed further by liming to protect the surface and to prepare the surface for subsequent application of lubricant prior to cold working or drawing. The improvement described in the aforementioned copending application resides in the development of a process wherein the various steps of descaling, Washing, liming and lubricating are provided in a single step wherein the steel is treated with a molten bath of sodium hydroxide and a reducing agent wherein the steel is descaled by chemical reduction and wherein the steel is heated to the desired temperature for advancing the steel through the die to effect reduction in cross-sectional area in accordance with the practice of this invention. Instead of applying molten salts for purposes of lubrication, use may be made of conventional lubricating compounds.

From the foregoing it will be apparent that a new and simplified metallurgical process has been developed for the production of steels having controlled warpage values, having improved machinability, improved surface characteristics and markedly increased strength properties. The development of steels having such tailor-made characteristics may be produced by the proper selection of chemistry, draft and temperature in a single operation thereby to produce steels incapable of being secured by processes heretofore employed other than by the use of multiple steps of working followed by heat treatment or strain relieving or by the use of more expensive and less available alloy steels. These other steels, in most instances, are incapable of having incorporated therein the various combinations of physical and mechanical properties which can be introduced into steel products by the simple metallurgical process herein described and claimed.

It will be understood that changes may be made in the details of processing and in the manner of heating and cooling of the steel during working as by drawing or extrusion without departing from the spirit of the invention, especially as defined in the following claims.

What is claimed is:

1. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, comprising the steps of descaling and lubricating the surfaces of the steel and drawing the steel through a drawing die to effect reduction in cross-sectional area while the steel is heated to a temperature within the range of 600-850 F. whereby physical and mechanical properties of the steel are improved.

2. The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing a hot rolled steel of the non-austenitic type having a pearlitic structurein a matrix of free ferrite and having a carbon content up to 0.65 percent by weight to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F. whereby the drawn steel is characterized by improvements in tensile strength, yield strength, hardness and proportional limits.

3. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, comprising the steps of descaling and lubricating the surfaces of the steel and extruding the steel through a die to effect reduction in cross-sectional area while the steel is heated to a temperature within the range of 600-850 F. whereby physical and mechanical properties of the steel are improved.

4. The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and extruding a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and having a carbon content up to 0.65 percent by weight to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F. whereby the extruded steel is characterized by improvements in tensile strength, yield strength, hardness and proportional limits.

5. The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and a carbon content within the range of 0.10 to 0.65 percent to effect reduction in cross-sectional area While the steel is at a temperature within the range of 600-850 F. whereby the steel is characterized by new and improved machinability properties.

6. The metallurgical process for the improvement of mechanical and physical properties of hot rolled steel in combination with improvements in its machining characteristics comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing a steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and having a carbon content within the range of 0.1 to 0.35 percent to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F.

7. The metallurgical process for the improvement of mechanical and physical properties of hot rolled steel which steel strain hardens and which hardens by some mode of precipitation when worked at a temperature between 600-850 E, comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing the steel through a draw die to effect reduction in crosssectional area while the steel is at a temperature of between 600-850" F.

8. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel which strain hardens and which hardens by precipitation when worked at a temperature between 600-850 F., comprising the steps of descaling the steel and lubricating I2 thesurfaces of the steeland extruding the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F.

9. The metallurgical process for the improvement of mechanical and physical properties of hot rolled steel including tensile strength, yield strength, proportional limits, hardness, ductility and machinaiblity in which the steel strain hardens and which hardens by some mode of precipitation when worked at a temperature between 600-850 F., comprising the steps of descaling the steel and lubricating the surfaces of the steel and advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F.

10. A steel product having improved machinability in combination with improved mechanical and physical properties produced by the method of claim 9.

11. The metallurgical process for improving the ma chinability of hot rolled steel and for the improvement of mechanical and physical properties of the steel in which the steel has a carbon content within the range of 0.1 to 0.5 percent and strain hardens and hardens by some mode of precipitation when worked at a temperature between 600-850 F., comprising the steps of descaling the steel and lubricating the surfaces of the steel and advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F.

12. In a metallurgical process for producing the properties of cold finished, hot rolled steel bars having improved mechanical and physical properties and wherein the hot rolled steel bars strain harden and harden by some mode of precipitation when worked at a temperature between 600-850 F., the steps of descaling the st el bars and lubricating the surfaces of the steel bars, and advancing the steel bars through a die to effect reduction in cross-sectional area While the steel is at a temperature within the range of 600-850 F.

13. In a metallurgical process for producing the properties of cold finished, hot rolled steel bars having improved mechanical and physical properties and wherein the hot rolled steel bars strain harden and harden by some mode of precipitation when worked at a temperature between 600-850 F., the steps of descaling the steel l bars and lubricating the surfaces of the steel bars, and

drawing the steel bars through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 600-850 F.

References Cited in the file of this patent UNITED STATES PATENTS Buchholtz May 8, 1934 OTHER REFERENCES 

1. THE METALLURGICAL PROCESS FOR THE IMPROVEMENT OF MECHANICAL AND PHYSICAL PROPERTIES OF A HOT ROLLED STEEL OF THE NON-AUSTENITIC TYPE HAVING A PEARLITIC STRUCTURE IN A MATRIX OF FREE FERRITE, COMPRISING THE STEPS OF DESCALING AND LUBRICATING THE SURFACES OF THE STEEL AND DRAWING THE STEEL THROUGH A DRAWING DIE TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA WHILE THE STEEL IS HEATED TO A TEMPERATURE WITHIN THE RANGE OF 600-850* F. WHEREBY PHYSICAL AND MECHANICAL PROPERTIES OF THE STEEL ARE IMPROVED. 